Magnetic drag tachometer



June 16, 1953 r J. H. ANDRESEN, JR 2,642,274

4 MAGNETIC DRAG TACHOMETER Original Filed July 25, 1946 2 Sheets-Sheet l I z z; I III 9 H Ill ,6

INV NTOR JOHN ,vpeese/y, J4.

ATTORN EYJ June 1953 J. H. ANDRESEN, JR 2,642,274

' MAGNETIC DRAG TACHOMETER Original Filed July 25, 1946 2 Sheets-Sheet 2 4 f3 /Z3 j 'r i' I 2 :4

.l7 f m! =|n IN; 34 I ill W (PW W ATTORN EY5 Patented June 16, 1953 UNITED STATES PATENT OFFICE MAGNETIC DRAG TACHOM'ETER John H. Andresen, J r., Port Washington, N. Y., as-

signor to Kollsman Instrument Corporation, Elmhurst, N. Y., a corporation of New York 4 Claims.

This application is a divisional application of my co-pending application Serial No. 686,168, now Patent No. 2,593,646. r

This invention relates to a magnetic drag tachometer for measuring rotative speeds and has for its object the provision of such tachometer where the relative movement between the magnetic field and the drag element has a substantial radial directional component to dampen movement of the drag element.

Another object of the invention is to provide a magnetic drag tachometer in which a drag disk presents a variable volume to the magnetic field to vary the response of the drag disk to change in rotative speed of the magnetic field.

Another object of the invention is the provision of a tachometer having a dra element with a pair of independently rotatable magnetic drag means cooperating therewith so that the movement of the drag element is determined by the algebraic sum of the rotative speeds of the magnetic drag means.

Other objects and features of the invention will be readily apparent to those skilled in the art from the specification and appended drawings illustrating certain preferred embodiments in which:

Figure 1 is a view partly in section and partly in elevation of a tachometer according to the present invention.

Figure 2 is a view similar to Figure l but showing the tachometer with two magnetic drag means.

Figure 3 is a detailed sectional view on the line IIIIII of Figure 2 indicating the pole faces on each of the magnetic disks of the magnetic drag means of the tachometers of Figures 1 and 2.

Figure 4 is a detailed horizontal view of a modified form of drag disk for the tachometer.

Figure 5 is a plan view of another form of drag disk for the tachometer.

Figure 6 is a plan view of still another form of the drag disk for the tachometer.

The tachometer shown in Figure 1 includes a supporting base I having attached thereto a cylindrical casing 2 closed by a glass 3 mounted on the casing 2 by a bezel 4 and sealed thereto by a gasket 5. In the base is disposed a bearing 6 in which is rotatably mounted a shaft 7 carrying a pair of permanent magnet disks 8 and 9 rigidly mounted to the shaft by a cast bonding medium. Each of the magnetic disks 3 and 9 have faces as indicated. in plan in Figure 3 being supplied with notches l l dividing the disk faces into a plurality of poles H which are magnetized so that adjacent poles are of opposite polarity. The magnetic disks 8 and 9 are mounted on the shaft 1 with poles of opposite polarity opposed to provide a strong magnetic field therebetween.

The base I is provided with a standard I3 carrying a supporting plate [4. In bearings l5 in plate I4 and It in the base I is pivotally mounted a shaft I'l upon which is rigidly supported a disk [6 of high conductivity material having a portion thereof projecting between the disks 8 and 9. Depending from the plate 54 is a support l9 to which and to the shaft I! is mounted a hairspring 2i biasing the shaft ll against rotation. The shaft I! terminates in a staff" 22 upon which is mounted a pointer 23 cooperating with a dial 24 mounted on the plate 54, the dial 24 hearing indicia of the quantity to be measured such as the rotative speed of the shaft 1.

Rotation of the shaft 1 and of the magnetic fields between the disks 6 and 9 results in a torque exerted on the disk l8 from the eddy currents induced therein. This torque is opposed by the bias of spring 2! and shaft I? will have an angular rotation to equalize the drag torque and the spring bias. With the uniform disk of Figure 1, the rotation of the shaft [1 will be proportional to the speed of rotation of the shaft 1. Rotation of shaft l'l moves the pointer 23 relative to the indicia on dial 254 to indicate the rota-tive speed.

With the shafts I l and l eccentrically mounted as shown, the relative movement between the magnetic field and the disk It will have a substantial radial directional component, the rela tive movement varying from substantially radial at the edge of the disk to substantially tangential at the inner penetration of the field. The radial directional component of relative movement does not affect the torque exerted on the disk is but does serve to dampen its movement to provide a steady position of the pointer 23 indicating the rotative speed. The tachometer of this invention thus secures the dampening effect from the rotating magnetic drag means itself without the necessity of additional elements such as stationary magnets cooperating with the drag element.

In the tachometer of Figure 2, the elements so far described are present except that base 3! has been modified to receive a second rotating magnetic drag Parts the same as in Figure l have been given the same reference numerals. In the base 3i there is provided a second bearing 32 in which is rotatably mounted a shaft 33 carrying a pair of permanent magnet disks 34 and 35 identical with the disks 8 and 9 and disposed at the opposite side of the shaft I! with the disk 18 similarly disposed between the pole pieces of the disks. Upon rotation of the shafts I and 33, two separate torques will be applied to the disk 18 by the eddy currents induced therein from the magnetic fields moving relative thereto. The resulting torque will be the algebraic sum of the individual torques and the movement of pointer 23 will be the algebraic sum of the rotative speeds of the shafts 1 and 33.

Nith a uniform drag disk, the pointer movement will be proportional to the rotative speed of the driven shaft and will be in uniform increments for uniform changes of rotative speeds. Where a .more sensitive pointer movement is desired at certain critical speeds, it is desired to render the scale on the dial 2d non-linear so as to expand it adjacent the critical value to secure greater pointer movement for a given change in rotative speed. The forms of drag disks illustrated in Figures 4, and 6 provide means for expanding or contracting the tachometer scale at rotative speed as desired. In Figure 4 the drag disk 35 secures the non-linear movement and scale by variation in its thickness to vary the value of eddy currents set up in the disk and hence to vary the change in torque on the disk for a given change in rotative speed.

In Figure 5 the drag disk 31 is indicated with a crescent 38 which may be cut out or material added on to the disk to secure the desired movement.

In Figure 6 the disk 39 has a portion of its periphery cut away as at M to vary the area and volume of the disk cooperating with the rotating magnetic field. It will be obvious that the drag disk may assume any structural shape producing a desired scale arrangement and pointer movement.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

I claim:

1. In a tachometer, a disk of high conductivity material, a rotatable shaft on which said disk is mounted, means biasing said shaft against rotation, indicating means operated by said shaft, magnetic drag means having a magnetic field passing through a portion only of the area of said disk, said area changing in location with movement of the disk, said disk having a nonuniform contour to vary at different speeds of said magnetic drag means the incremental movement of said disk in response to incremental change in speed of rotation of the drag means; said non-uniform contour being a variable radius.

2. In a tachometer, a disk of high conductivity material, a rotatable shaft on which said disk is mounted, means biasing said shaft against rotation, indicating means operated by said shaft, magnetic drag means having a magnetic field passing through a portion only of the area of said disk, said area changing in location with movement of the disk, said disk having a nonuniform contour to vary at different speeds of said magnetic drag means the incremental movement of said disk in response to incremental change in speed of rotation of the drag means; said non-uniform contour being a combination of a variable radius and thickness.

3. In a tachometer, a disk of high conductivity material, a rotatable shaft on which said disk is mounted, means biasing said shaft against rotation, indicating means operated by said shaft, magnetic drag means having a magnetic field passing through a portion only of the area of said disk, said area changing in location with movement of the disk, said disk having a non-uniform contour to vary at different speeds of said magnetic drag means the incremental movement of said disk in response to incremental change in speed of rotation of the drag means; said nonuniform contour being a combination of a variable radius and thickness, said disk having a portion thereof removed to aid in producing the required non-linear effect.

4. In a tachometer, a disk of high conductivity material, a rotatable shaft on which said disk is mounted, means biasing said shaft against rotation, indicating means operated by said shaft, magnetic drag means having a magnetic field passing through a portion only of the area of said disk, said area changing in location with movement of the disk, said disk having a non-uniform contour to vary at different speeds of said magnetic drag means the incremental movement of said disk in response to incremental change in speed of rotation of the drag means; said nonuniform contour being a variable radius, said variable radius varying in a linear manner with the polar angle eifecting an oscillatory motion.

JOHN H. ANDRESEN, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,309,390 Young July 8, 1919 1,989,547 Clark Jan. 29, 1935 2,549,754 Bosch Apr. 24, 1951 

